1. Field of the Invention
Embodiments of the invention generally relate to deposition of a semi-conductive layer onto a substrate. More specifically, the invention relates to a method of depositing a refractory metal layer using a cyclical deposition technique.
2. Description of the Related Art
The requirements of sub-quarter micron semiconductor devices with their VSLI or USLI integration necessitate using various layers, e.g., conductive layers and insulating layers. Typically, conductive layers are interconnected through features such as horizontal lines and vertical contact holes, vias, trenches, or openings in the insulating layer by a damascene or dual damascene process. With higher integration and increased device speed, the size of these features demands to be small, such as less than 0.25 micron of aperture, while the aspect ratio of the features, i.e., their height divided by width, needs to be greater than 5:1, and even greater than 10:1.
In the fabrication of semiconductor devices, such as dynamic random access memories (DRAMs), static random access memories (SRAMs), microprocessors, etc., insulating layers or barrier layers are used to separate conductive layers and prevent the diffusion of one material into an adjacent material. For example, diffusion barriers are needed to prevent copper diffusion, especially when an underlying low dielectric-constant dielectric layer is used. Low dielectric-constant materials are often soft and porous, and adhere poorly to adjacent materials. Therefore, a good barrier/adhesion layer is required for processing a low resistivity conductive layer, such as a copper layer, compatible with low dielectric-constant materials.
Diffusion barriers are also used to prevent undesirable reactions between conductive layers, such as spiking when aluminum contacts silicon surfaces, for example, and the formation of highly resistive alloy when aluminum comes into direct contact with tungsten. Further, diffusion resistant materials are used as adhesion or encapsulation materials or gate electrode liners for the high dielectric-constant dielectric layer in DRAM application.
Barrier/adhesion layers containing refractory metal materials are commonly used for VLSI and ULSI devices. Refractory metal materials with good adhesion properties to conductive layers, such as those containing titanium (Ti), tantalum (Ta), tungsten (W), titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride (WN), etc., have been used in integrated circuit manufacturing to form liner/barrier layers.
Furthermore, a ternary refractory metal material such as refractory metal silicon nitride, e.g. tantalum silicon nitride (TaSiN) and titanium silicon nitride (TiSiN), forms a superior barrier layer/adhesion layer over a binary refractory metal material such as tantalum nitride, titanium nitride, or tungsten nitride. The incorporation of silicon into a tantalum nitride layer by metalorganic chemical vapor deposition (MOCVD) to form a tantalum silicon nitride layer has been shown to provide as a better diffusion and/or insulation barrier for copper interconnects than tantalum nitride barriers. Also, the incorporation of silicon into a titanium nitride layer to form a titanium silicon nitride layer helps to prevent fluorine diffusion for the subsequent tungsten application tungsten fluoride (WF6) as precursor. However, such deposition methods are performed at higher temperatures which may not be desirable for some applications, and have trouble controlling the composition of the barrier/adhesion layer, such as the ratio of the materials incorporated.
In addition, traditional deposition processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), have difficulty in filling high aspect ratio features and often result in poor step coverage, poor conformality, and byproduct formation. The complicated topography of devices with high aspect ratios requires precise control over film properties such as composition, thickness, morphology, and electrical characteristics. For example, conventional fabrication of titanium nitride adhesion layers used as tungsten liners often results in high and unpredictably variable contact resistance of the finished tungsten contact following fabrication. Typically, titanium nitride is deposited by decomposing a metalorganic compound of titanium using conventional CVD or PVD processes and may contain carbon and oxygen impurities, resulting in an increase in resistivity of the adhesion layer. In addition, the carbon and oxygen impurities in the titanium nitride layer may react with the byproducts of a subsequently deposited tungsten plug CVD process after the reduction of tungsten fluoride (WF6) or tungsten chloride (WCl6) compounds by silane, resulting in the localized formation of nucleated insulating structures.
Cyclical deposition techniques such as atomic layer deposition (ALD) and rapid sequential chemical vapor deposition provide a better degree of control over substrate surface reactions and is suitable for the deposition of material layers over features having high aspect ratios to provide good step coverage. One example of forming a binary material layer using a cyclical deposition technique comprises the sequential introduction of pulses of a first precursor/reactant and a second precursor/reactant. For instance, one cycle may comprise a pulse of the first precursor, followed by a pulse of a purge gas and/or a pump evacuation, followed by a pulse of a second precursor, and followed by a pulse of a purge gas and/or a pump evacuation. Sequential introduction of separate pulses of different precursors results in the alternating self-limiting surface adsorption or chemisorption of the precursors on the substrate surface and forms a monolayer or less of the binary material for each cycle. In this way, thin films are grown as a monolayer or less at a time to form a deposited layer or film, e.g., a tantalum nitride layer using a tantalum-containing precursor and ammonia gas as precursors.
Although the deposition rate is slower in cyclical deposition processes than conventional CVD and PVD processes, deposition can be conducted in a simplified chamber/reactor where process conditions such as gas flow and deposition temperature are not as critical. Further, cyclical deposition processes can be performed at lower temperatures and can use a wider range of precursors. A satisfactory apparatus and method for cyclical deposition techniques have not been established to form conformal layers of ternary materials utilizing three precursors.
There is a need, therefore, for a repeatable and controlled method of depositing a ternary metal silicon nitride layer.